The site is 100% free and even ad-free. It is my hobby project and I just enjoy helping others, meeting interesting people and learning while developing it.
Looks like loneliness is widespread in the FIRE community especially during the current times, so there is a large demand for meeting like minded folks.
It took me at least 517 hours and 211$ so far, but I met a lot of people and learned so much. It definitely gets harder and harder to continue developing it on my own, since the code base and complexity grows. But I try to fight that and use more ready-made solutions.